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Learn more about combined sewer overflow (CSOs) by scrolling through our interactive storyboard below.
Learn more about combined sewer overflow (CSOs) by scrolling through our interactive storyboard below.
A Combined Sewer Overflow (CSO) occurs during and after wet weather like a rainstorm or snowmelt. Because the city is made of impervious surfaces, such as asphalt and concrete, most stormwater canʼt be absorbed into the ground, like it would when it falls on soil in a park or garden. Stormwater runs off hard surfaces into storm drains that eventually join up with the sewer pipes leading to one of NYCʼs sewage treatment plants. This system often exceeds capacity, and the combination of stormwater and sewage must be diverted – without treatment – to the nearest creek, river or bay through a CSO outfall. CSO events happen about 100 times a year, and discharge more than 20 billion gallons of wastewater into the City's creeks, rivers and bays.
Brooklyn’s Gowanus neighborhood is one of the most vulnerable areas in the city to CSO, with the Gowanus Canal receiving untreated waste from sewer overflows during most heavy rain events of a season. Not only is the canal one of the nation’s most seriously contaminated water bodies, but the Gowanus neighborhood is also susceptible to flooding, which in the event of a Hurricane Sandy-level storm will result in untreated waste flooding neighborhood streets. The severity of the situation led the U.S. Environmental Protection Agency (EPA) to begin a Superfund cleanup to revitalize the waterway and improve the supporting wastewater infrastructure. Many, however, believe that the progress being made by the EPA will be short-lived as the city has announced plans to transform the low-rise industrial area to a hub of residential development.
CSO Connect Gowanus is a unique community-based project with the goal of providing transparency and clarity to the issues and the work surrounding the Gowanus Canal sewer system. The project uses publicly accessible data from NYC Dept. of Environmental Protection to create an interactive map that displays a more complete picture of how the sewer system works and how the City is going to improve it.
Click on the menu of the map below to show the hidden layers depicting existing and planned infrastructure projects. These projects will reduce the amount of CSO into the Gowanus Canal.
Though there are plenty of infrastructure projects existing and planned, CSO remains to be a major threat to its receiving waterbody. The map below shows the water quality at different sampling points in Brooklyn in June 2019. Click on the sampling point to view the comments from DEP.
Source: Department of Environmental Protection, Open Sewer Atlas
In early 2019, the City released its Gowanus rezoning proposal, which calls for denser towers, affordable housing, and taller structures. Of concern to many is the projection that the proposed rezoning is expected to lure 18,000 new residents to the neighborhood, without factoring in mitigation for the surge of sewage created by that increase in population. The Census Bureau estimates that 23,000 people currently live in Gowanus; the projected population increase resulting from the rezoning would nearly double the local population (an increase of 78%).
Source: Gowanus Canal Conservancy, SWIM Coalition
Join the Gowanus CSO Connect community and commit to doing your part in reducing the untreated sewage that enters the canal during heavy rains. Simply select your location on the map below, enter your name, and choose the contribution you will make to prevent CSO! Now others can see the good you are doing to keep Gowanus a clean and healthy neighborhood. To share your commitment and encourage others to join the movement, share this link and ask your friends to mark their contribution on the map as well.
Cover photo credit: DLANDstudio
Facing the heavily contaminated Gowanus Canal, the United States Environmental Protection Agency (EPA) added it to the Superfund program’s National Priorities List on March 2, 2010. Based upon the results of an extensive investigation of the contamination in the Canal and public comment on a proposed remedy, in September 2013, EPA finalizing a plan to clean up the contaminated sediment that has accumulated as a result of CSO discharges. The remedy also includes the construction of retention tanks to reduce the volume of contaminated sewage solid discharges from CSOs at two major outfalls in the upper portion of the Canal be outfitted with retention tanks. The cost of the cleanup plan is estimated to be $500 million.
In December 2018, it is reported that the City’s $53 Million investment in Gowanus neighborhood is secured to improve drainage and the health of the Canal. The additional capacity in the neighborhood’s drainage system is helping to reduce roadway flooding and the amount of pollution that may be discharged into the Gowanus Canal during heavy rainstorms. Funding for the project is provided by Department of Environmental Protection (DEP) while Department of Design and Construction (DDC) is managing the construction.
On January 30, 2019, the Department of City Planning (DCP) released the draft Gowanus zoning proposal based on extensive outreach and planning with local elected officials and community members. The Gowanus Canal will become the centerpiece of a green, resilient neighborhood with new, sustainable, mixed use development boasting more open space and parks and community resources
The projected increase in density will add more sewage load to CSO sheds, causing more frequent overflows. The added density proposed in the DCP Draft Zoning Plan will result in a substantial increase in wastewater generation and sewage overflow into the Canal. Existing and currently planned infrastructure investments do not address this issue. That’s why we need your action!
